286 ALLUVIUM. 



sitviated upon its borders, lead to the opinion, that in distant ages, it 

 was covered either by an arm of the sea, or an inland marine lake, which 

 extended up the country far beyond the town of Lewes ; the site of the 

 cHff being buried beneath its waters. During the last century, and 

 before the present improved state of the navigation of the Ouse, the 

 levels were annually exposed to extensive inundations, from the over- 

 flowing of the banks of the river ; the rhies and other eminences, forming 

 islands in the midst of the lake. 



A section of this alluvial deposit exposes, 



1. Pipe clay; the detritus of the chalk marl upon which it 



reposes, ----.__- i foot. 



2. Silt, or blue clay, with marine and fresh water shells ; 



from - - - - - - - 5 to 25 feet. 



3. Impure peat, with trunks of trees, _ - _ - 5 feet. 



4. Vegetable mould, -____-- 1 foot. 

 Interspersions of white sand, gravel, and chalk rubble, also occur in 



various places. 



The pipe clay is sufficiently plastic for the usual purposes to which 

 that substance is applied, and is evidently the detritus of the chalk 

 marl. 



The silt varies in thickness from three to twenty-five, and in some 

 instances, to thirty feet. The lower part of the bed contains marine 

 shells ; the upper, fresh water shells ; but in the intermediate layers, both 

 kinds are indiscriminately mixed together. The shells correspond with 

 the recent testaceee of the adjacent river, and sea ; and I believe, are 

 common in other alluvial depositions near the coast. I am indebted to 

 William Wood, Esq. F.K.S. &c. (of the Strand), for the following deter- 

 mination of their characters. 



